Many types of batteries and other power cells are known, based upon a relatively wide range of electrical couples. Among the most popular electrical couples are those containing zinc. Zinc is regarded as the highest energy couple component that can be cycled in an aqueous room temperature battery and is therefore commonly used in numerous battery and power cell applications.
For example, zinc is coupled with carbon in most simple flashlight batteries to provide a relatively inexpensive and reliable power source. Although manufacture of Zn/C batteries is generally simple and poses only relatively little environmental impact, various disadvantages of Zn/C batteries exist. Among other things, the ratio of power to weight in commonly used Zn/C batteries is relatively poor. To improve the ratio of power to weight, alternative coupling partners and systems can be employed. For example, zinc can be coupled with mercury oxide or silver to achieve an improved power to weight ratio. However, the toxicity of mercury oxide is frequently problematic in manufacture and tends to become even more problematic when such batteries are discarded. On the other hand, while silver as a coupling partner for zinc is environmentally substantially neutral and significantly improves the power to weight ratio, the use of silver is in many instances economically prohibitive.
Furthermore, halogens may be employed as a coupling partner for zinc, and most common zinc-halogen couples include zinc-bromine and zinc-chloride (e.g., for load leveling batteries). However, such battery configurations are often difficult to integrate into portable or miniaturized devices. Moreover, such battery configurations typically require pumping systems and are often prone to leakage leading to significant problems due to the highly corrosive nature of halogens.
Alternatively, oxygen may be employed in primary batteries as a gaseous redox partner for zinc, thereby generally avoiding problems associated with toxicity, excessive cost for redox partners, or spillage. Among various advantages in such configurations, using air (i.e., oxygen) as redox partner for zinc typically results in a relatively high power to weight ratio. Moreover, the zinc-oxygen system generally provides a relatively flat discharge curve. However, reasonable shelf life of such primary batteries can often only be achieved by using an airtight seal, and commercial applications of zinc-air batteries have previously been limited to primary or non-rechargeable types.
In order to further take advantage of the relatively high power-to-weight ratio in zinc air batteries, secondary zinc air batteries have been developed. However, among various other difficulties, electrodeposition of metallic zinc during charging frequently resulted in dendrite formation, thereby changing the zinc electrode shape and consequently decreasing the battery capacity. To reduce at least some of the problems associated with dendrite growth in alkaline electrolyte, various compositions, configurations, and methods have been developed. For example, mechanical movement of the anode to prevent or reduce dendrite growth is described in U.S. Pat. No. 3,716,413 to Eisner, U.S. Pat. No. 3,560,261 to Stachurski et al, or in U.S. Pat. No. 3,440,098 to Stachurski.
Alternatively, complexing agents may be added to the electrolyte to increase solubility of the zinc in the alkaline electrolyte and to thereby improve the quality of the plating as described in U.S. Pat. No. 3,540,935 to Keating et al. In yet another approach to reduce or inhibit dendrite formation on the zinc anode, the anode surface may be mechanically abraded while the alkaline electrolyte is vigorously moved within the battery as described in U.S. Pat. No. 3,822,149 to Hale et al.
However, despite at least some reduction in dendrite formation using the above compositions, configurations, and methods, additional difficulties nevertheless remain. Among other things, the use of alkaline electrolytes frequently leads to absorption of carbon dioxide from the air and other sources, which will consequently form carbonates in the electrolyte, which in turn tend to reduce conductivity and clog the pores in the active surfaces of the electrodes.
To avoid at least some of the problems associated with the used of alkaline electrolytes in zinc air batteries, acidic aqueous electrolytes may be employed. For example, acid electrolytes have been used in primary or non-reversible electrochemical cells as described in U.S. Pat. No. 3,825,445 to MacKarthy. Where rechargeable zinc air batteries are desired, dendrite formation may be reduced to at least some extent using a zinc-containing electrolyte comprising an aqueous acid and containing a quaternary ammonium compound for suppression of formation of dendrites on the anode during charging as described in U.S. Pat. No. 3,944,430. However, quaternary ammonium compounds may adversely affect longevity of the battery and may further be oxidized over time. Moreover, the relatively limited solubility of zinc ions in such electrolytes may further reduce the capacity of the battery.
Alternatively, the electrolyte in zinc air batteries may be vigorously circulated to avoid or at least reduce dendrite formation as described in U.S. Pat. No. 4,220,690 to Blurton et al. While Blurton's configuration reduces dendrite formation to at least some extent, continuous pumping of the electrolyte is typically required. Furthermore, Blurton's configuration typically requires separate catholyte and anolyte reservoirs, thereby rendering the battery more space consuming and increasing the weight of such battery systems.
In yet further alternative approaches, zinc air batteries may be mechanically recharged by replacing the depleted zinc anode and zinc enriched electrolyte with an externally regenerated zinc anode and acid electrolyte (e.g., Creation of a zinc/air-battery-system-infrastructure for the European union (ZABEU) EU Project TR/00013/94). Mechanically recharging zinc air battery systems generally avoids dendrite formation within the battery, however, requires availability of spare anodes and electrolyte at the point of recharge, which may pose a significant logistic problem for everyday use of secondary rechargeable zinc air batteries.
Thus, although there are numerous coupling partners for zinc in batteries and power cells known in the art, all or almost all of them suffer from one or more disadvantage. Therefore, there is still a need to provide compositions and methods for improved batteries.